The process of drilling a hole in the ground for the extraction of a natural resource requires a fluid for removing cuttings from the wellbore, controlling formation pressures and maintaining hole stability. Drilling through oil sand formations causes problematic accretion of tar on drilling apparatus. Bitumen accretion on metal surfaces impairs drilling operations by blinding shale shaker screens, plugging centrifuges and drill bits, torque and drag increase and stuck pipe or casing. Standard drilling practices through oil sand formations, which are generally unconsolidated, can also lead to hole instability problems.
If these formations are drilled horizontally, torque and drag between the formation and the drill string can limit both the rate of drilling and the ultimate length of the horizontal section that can be achieved.
Solvents, surfactants and viscosifiers have been used in drilling fluids for drilling through heavy oil, including bitumen-containing formations. In addition, or alternately, drilling fluids have been chilled to deter accretion and enhance hole stability.